Conventionally, an image that includes a moving image and graphics was constituted by capturing a frame image of the moving image and combining the graphics with the frame image, which is treated as a still image. However, the use application of images, the data format and the type of drawing process required differ between moving images and graphics. For example, in the case of moving images, a technique that prevents a reduction in moving image quality due to dropped frames or the like is sought. The systems for processing moving images and graphics are therefore separated, and the output results of the respective processing systems are composed and output.
Japanese Patent Laid-Open No. 07-72850, which relates to an image forming apparatus that composes and outputs a moving image and graphics, proposes a method for composing graphics data and moving image data stored in memory while switching the readout addresses in memory. Japanese Patent Laid-Open No. 2005-321481 proposes achieving high quality video by keeping a video signal processing function independent from a graphics controller, and inputting images created by the graphics controller as video signals.
However, while the respective quality of moving images and graphics can be enhanced according to the above-mentioned conventional methods since the systems for processing a moving image and graphics are separated, in the case where a moving image and graphics are displayed so as to overlap, a plurality of buffers are needed for storing the graphics drawing results in order for display to be performed correctly. The resultant increase in device cost was problematic.